Inhibitor



Feb. 7, 1939. J. R, TQTTLE 2,146,162

INHIBITOR Filed Oct. l5, 1956 Patented Feb. 7, 1939 UNITED STATES PATENT GFFICE mHlBITOB John Ross Tuttle, Summit, N. J., asslgnor to General Chemical Company, New York, N. Y., a corporation of New York Application October 15,

11 Claims.

This invention relates to corrosion inhibitors. to inhibited acid compositions, to methods for pickling metals for the removal of oxides or mill g scale, and to pickling baths. 'Ihe invention is more particularly directed to inhibitors, inhibited acid solution and pickling baths comprising or containing sulfur bearing oils derived from sludges formed in oil reflning processes in which sulfuric acid is employed. The invention is also especially directed to metal pickling processes carried out with the utilization of such sulfur bearing oils as corrosion inhibitors.

Pickling solutions for removing oxides or mill scalefrom the surface of metals ordinarily consist very largely of a dilute solution of an inorganic acid such as sulfuric acid. The acid, although it dissolves the oxides and scale, also attacks the metal to some extent so that the acid is largely consumed and a certain amount of metal is lost. It also appears that the hydrogen liberated by the action of the acid on the metal has a serious embrittling eiect upon the metal being treated. VInhibitors are used not only for the reasons noted but also to prevent pitting and corrosion where the metal is not covered by scale. Inhibitors are commonly employed in such solutions to decrease the activity of the acid with respect to the metal without greatly affecting the solvent action of the solution with respect to the oxides.

The principal objects of the invention are directed to improvements in inhibited acid compositions, methods for pickling metals, pickling baths, and to the provision of sulfur bearing oil corrosion inhibitors for these purposes. It is a further aim of the invention to provide sulfur bearing corrosion inhibitor oils having a relatively high sulfur content substantially all of which is in strong chemical combination, and which oils are stable and do not become turbid or deposit sulfur on standing.

In oil refining processes, involving treatment of petroleum distillate oils with sulfuric acid, large quantities of sludges are produced. When destructively decomposed by heating, these sludges form gas mixtures containing water vapor and condensable hydrocarbon vapors, and gases such as 'sulfur dioxide, carbon dioxide, nitrogen and uncondensable hydrocarbons.

The invention comprises corrosion inhibitors, inhibited acid compositions, and particularly metal picklingprocesses and pickling baths. According to the present invention, it has been discovered that when sludge material, resulting from treatment with sulfuric acid of relatively light hy- 1936, Serial N0. 105,653

(ci 14s-s) drocarbon oil distillates containing substantial quantities of sulfur compounds, is dissociated preferably by destructive decomposition by heating to form a hot gas mixture containing hydrocarbon vapors and the gas mixture is cooled, for example to about normal temperature, an oily condensate is obtained which is a sulfur bearing oil possessing properties rendering the oil especially suitedvfor inhibiting the corrosive action of acids on metals. The oils so produced are light colored, light bodied, stable oils, high in sulfur in strong chemical combination, and do not become turbid or deposit free sulfur on standing.

A further appreciation of the objects and advantages of the invention may be had from a consideration of the following description of the oils constituting the improved corrosion inhibitors, of inhibited acid compositions and pickling baths containing the improved inhibitors, of pickling methods involving use of the improved sulfur bearing oil inhibitors, and of methods for making the improved inhibitors. The accompanying drawing illustrates diagrammatically apparatus by which the improved sulfur bearing oil inhibitors may be made.

Referring to the drawing, I0 indicates the combustion chamber of a furnace adapted to burn coal, coke, oil, natural gas and other fuel. Mounted in chamber Il! is a decomposing kiln or retort II of any desired construction, for example a iixed shell provided with suitable mechanism such as a screw conveyor, not shown, to facilitate discharge of coke. A rotary retort may also be employed if desired. Preferably an externally heated kiln adapted to substantially exclude admission of air is used. One end of kiln II communicates with a gas outlet I3, and the opposite end projects into a header I4 into which the solid residue of the zdecomposition of the acid sludge is continuously discharged. Header N empties into air-lock I5 through which coke may be discharged without admitting air to the kiln. Acid sludges, constituting sources of the inhibitor oils of the invention, are run into the kiln from supply tank Il through a valve-controlled pipe I8. Gas outlet I3 is connected to the lower end of a cooler or condenser of any suitable construction, either air or water cooled, and operated so as to reduce the temperature of the gas stream to substantially normal to condense the bulk of the water vapor and a major portion of condensable hydrocarbons contained in the gas. condensate from the cooler drains into a separator or collecting tank 2| through a pipe 22 having a liquid seal.

I'he gases uncondensed in cooler 20, containing principally sulfur dioxide, are discharged through gas line 23, and maybe used as desired, for examplein the manufacture of sulfuric acid by the contact process.

Separator 2| may be a tank or vat large enough to permit continuous gravity separation of water and oil contained in the condensate discharged from condenser 20. The sulfur bearing hydrocarbon oils of the condensate rise to the top of the mass in the separator, and may be withdrawn continuously or intermittently through pipe 25 discharging into a collecting tank 26. Water settling to the bottom of the separator may be drawn oi through pipe 21, controlled by valve 2B, and discharged to waste or otherwise disposed of.

The still 30, of any approved construction, may

- be externally heated by hot combustion gases generated in brickwork setting 3|. Raw condensate from collecting tank 26 is run into the still through pipe 38, controlled by valve 39. Vapors generated in the still now through line 4| to a condenser 43, the condensate of which drains through pipes 45 and 46, into receivers 50 and 5|.

The improved inhibitor oils of the invention may be made in apparatus such as illustrated in the drawing and described above by operating substantially as follows.

In producing the improved inhibitors, acid sludges which may be employed are those resulting from sulfuric acid treatment of light distillate oils obtained from petroleum crudes containing sulfur. The acid sludges employed in making the inhibitor oils of the present invention are preferably sludges resulting from treatment with sulfuric acid of light hydrocarbon oil distillates 'such as gasoline and kerosene, containing not less than about 0.15% sulfur, although distillates containing less sulfur may be employed if desired. Illustrative examples of distillate oils from which sludges are produced of a character suitable for use in the present invention are straight-run gasoline distillates containing about 0.15%' sulfur or more, and

cracked distillate averaging 0.25 to 0.30% sulfur or more.

Sludge material of the type indicated and which may have "for example a titratable acidity of 40% to 60% expressed as H2SO4 is continuously fed into kiln from supply tank I1. The burners in furnace |0 are adjusted to maintain within the kiln temperatures desirably not in excess of about 750 F., as above this temperature the sulfur oils constituting the inhibitors of the present invention tend to be decomposed. The preferred temperatures are about 250 F. at the sludge inlet end, and about 500 F. to 600 F. at the coke outlet end of the kiln.

The sludge, gradually passed through the retort', is relatively gradually heated through the preferred temperature range and `is decomposed by the action of heat, and the free and/or combined sulfuric acid of the sludge is reduced to sulfur dioxide by the hydrogen of the hydrocarbons and/or by the carbonaceous matter contained in the sludge. The sludge material is then dissociated, as by the destructive distillation method indicated, with production of water vapor, and hydrocarbon vapors and sulfur compounds are formed. Residual coke is continuouslydischarged from the kiln through air-lock I5. .The maior part of the inhibitor oils of the invention appear to have been evolved by the time the sludge has reached a temperature oi'` The gas resulting from the decomposition of the sludge contains principally water vapor and sulfur dioxide, substantial amounts of condensable hydrocarbons and sulfur compounds, and smaller quantities of uncondensable hydrocarbons and gases such as carbon dioxide, carbon monoxide, and nitrogen. For example, one representative sludge having a titratable acidity of about 50% expressed as HzSOi yielded on decomposition by destructive distillation about 28% residual coke, and a retort gas which, after cooling to about normal temperatures, produced about 6% condensable oils, about 35% water, based on the weight of the sludge, balance of the retort gas comprising sulfur dioxide, carbon dioxide, carbon monoxide, nitrogen and uncondensable hydrocarbons and water vapor. As previously noted, according to the preferred way for making the sulfur bearing oil inhibitors of the invention, decomposition of sludges is eected in the kiln substantially in the absence of oxygen and in the absence of other extraneous gases. When so operating, the volume of gas formed is lessened and loss of oil by volatilization is decreased.

'I'he hot gaseous and vaporous products of decomposition of the sludge are discharged from the kiln and passed through conduit |3 into condenser 20 in which the gases are cooled to substantially normal temperatures. Cooling may be accomplished by circulating through the condenser in indirect heat exchange relation with the retort gas mixture any suitable cooling liquid or gas. In place of the condenser illustrated in the drawing, a vertical tower having a spray head at the top for introduction of water may be employed. In such cases, the retort gas mixture is introduced into the bottom of the tower and flows upwardly, intimately contacting and mingling with the downwardly directed spray of water fed in at the top of the tower. The amount of cooling water introduced is so controlled as to cool the exit gases leaving the top of the tower to about normal atmospheric temperatures.

During cooling of the retort gas mixture in the condenser 20, substantially all of the water vapor and the major portion of the condensable hydrocarbon vapors and sulfur compounds are condensed out of the gas stream. The condensate of cooler 20, containing varying proportions oi' water and liquid hydrocarbons and sulfur compounds, is drained through pipe 22 into separator 2|. In the latter, the oils rise to the top of the liquid mass in the tank, and may be intermittently or continuously withdrawn through pipe 25 into tank 26 for collecting what may be termed a raw condensate or initial sulfur oil. The water settling to the bottom of the separator 2| may be discharged from the system through pipe 2l.

' The oil vcollecting in tank 26 is an oil containing generally from about 3 to about 22% sulfur, apparently in strong chemical combination. It will be understood the sulfur content of this condensate may vary considerably in accordance with the characteristics of the initial crude oils and of the acid sludges produced on treatment of the hydrocarbon oil distillates with sulfuric acid. For example, an acid sludge formed through sulfuric acid treatment of a straight-run gasoline yielded an oil condensate of 12% by weight of A weight of oil condensate having a sulfur content of 7.5%. In another instance, a cracked distillate averaging about .25 to .30% sulfur produced -on treatment with sulfuric a sludge-which,

on treatment in accordance with the present method, yielded 10.8% by weight of oil condensate analyzing 20.8% sulfur.

According to the invention, it has been found that oils produced are sulfur bearing oils having properties making such oils especially suited for use as corrosion inhibitors. If desired, the raw condensates recovered in tank .26 may be employed directly asinhibitors in inhibited acid compositions, pickling baths, and in pickling processes. However, the oil in this state contains appreciable quantities of foreign matter, such as coke dust and tars, which under some circumstances may be desirably removed. Further, the oil collecting in tank 26 comprises several low and high boiling fractions. It will be understood the raw condensate of tank 26, the raw condensate of tank 26 with foreign matter such as coke dust and tars removed, a light fraction of the raw condensate or a heavy fraction of the raw condensate are suited for use as corrosion inhibitors.

Removal of foreign matter from the raw condensate of tank 26 and splitting of the condensate into two or more fractions may be done by distillation. For this purpose, oils from tank 26 are run into still 30 through line 38. The distillation operation may be carried out in any suitable still, preferably one provided with equipment for collecting separate fractions of distillate. From the above, it will be understood distillation of the raw condensate is principally for two purposes, rst, to remove coke and tars from the oil, and second, to produce preferably two fractions,

, one having a relatively low boiling range, and another fraction having a higher boiling point range. Distillation may be effected for example by external heating of still 30. If desired, distillation of the crude condensate may also be accomplished at temperatures lower than those hereinafter mentioned by introducing live steam directly into the oil body while externally heating the same. Distillatioirmay also be effected, though possibly less desirably, by superheated live steam, using steam at slightly above atmospheric pressure and heated to say 225-250 F. before introduction into the oil. Vacuum distillation may be employed if desired.

Still 30 may be operated to produce a first cut including all the oils distilling over at temperatures up to about 350 F. at normal pressure. Vapors generated within this temperature range are liquefied in condenser 43, and are run into receiver 50. This relatively low boiling fraction may for example constitute approximately 20% by weight of the raw condensate fed into still 30. When removal of these low boiling fractions -from the oil in still 30 is substantially complete,

the temperature is raised to distill over oils having boiling points ranging from about 350 F. up to about 650 F. Vapors formed are condensed in cooler 43, and may be recovered in receiver 5l. This high boiling fraction may comprise for example 60-66% by weight of the raw condensate introduced into still 30. Roughly 10% by weight of the original raw condensate withdrawn from tank 26 may remain as a coke or asphalt residue in the still, and around 5-10% by weight of the original raw condensate may be lost in the distillation operation as uncondensable vapors and gases. The low boiling cut recovered in receiver BEST AVAILABLE COPY 3 50 contains a slightly higher percentage of sulfur than the higher boiling fraction collected in receiver 5|. If desired, all of the vapors evolved in still 30 may be condensed and collected in a single receiver instead of in two receivers as 50 and 5I. In this situation, while there is some decomposition with liberation of H28, the condensate collected corresponds in a general way with the condensate collected in tank 26 except that foreign matter, such as coke dust and tars, have been removed,

Any of the foregoing oils may be used as inhibitors, directly as collected in tank 26, or as collected as a single fraction from condenser 43, or as collected in receiver 50 or 5|. The oils, however, apparently contain substances such as pyridines and mercaptans which impart to the oils undesirable odors and which tend to render the oils somewhat unstable on standing. Accordingly, it is preferred to further treat the oils to stabilize the same and remove odors. This may be accomplished by treating the oils with a solution of caustic soda or sulfuric acid or both. When employing caustic alkali the oil may be agitated with a 20% caustic soda solution at temperatures of about 190 F. until reaction appears complete. The reaction products are allowed to settle, and are withdrawn. The oil may then be washed with water to remove traces of alkali, and brightened as by blowing with air.

'I'he oils may also be stabilized by treating with sulfuric acid, say about equal Volume and washed with water and alkali to remove traces of acid. It is preferred to use acid of concentration not in excess of about 60% H2SO4, since acid of this or less 'concentration does not appear to have appreciable effect on the desired sulfur compounds which should preferably be retained in the product. If desired, the oils may be stabilized by using acid of greater concentration, say up to about 93.2% H2804 (66 B.) in which case the amount of stronger acid should not desirably exceed about '7% by volume of the oil treated.

Treatment of the oils with either caustic alkali or sulfuric acid notably improves the odor and increases the stability of the oils. In some instances, it is preferred to subject the oils to treatment with both caustic alkali and sulfuric acid.

In this case, after subjecting the oils to the caustic soda treatment noted above, and removing the alkali extract, the oils are washed with Water to remove the alkali, and then treated. with one or more washes of equal volume of dilute sulfuric acid, for example 30% H2SO4. -The nal oil products may be washed with water to remove traces of acid, and then brightened by blowing with air, or by other methods.

. In the case where the foreign matter is removed from the condensate of tank 26, as by distillation and collection of all the distillate in a single receiver connected to condenser 43, the resulting oil may be stabilized as described.

The oils stabilized, for example as mentioned above, are sulfur bearing mineral oils, light bodied, and have a high sulfur content, substantially all of which is in strong chemical combination. It appears substantial amounts of the contained sulfur is present as alkyl suldes and possibly also some di-sulfldes, and other sulfur bearing compounds.v The sulfur content Varies from about 3 to about 22%. The'oils on standing do not become turbid or deposit sulfur. The oils are a light straw color, and the specific gravity of a representative oil is about 0.98. The viscosity is low, about 32 to 34 Saybolt at 100 F.

In accordance with the invention, the sulfur bearing oils described, comprising the raw condensate of tank 26, the raw condensate of tank -26"distilled to remove'foreign matter such as and in metal picklingprocesses.

The acid pickling baths with which the improved sulur oil inhibitors of the invention are used may be acid baths having an HzSOr concentration of say 6 to 10%, such as are customarily employed for pickling and cleaning iron or steel. Other acid baths, such as acid sulfate baths may be used if desired. The amount of the sulfur bearing oil inhibitor added to the bath for carrying out the pickling or cleaning operation may be varied. As a rule only a small amount of the sulfur bearing oil inhibitor is required. For example, the bath may contain from about 1 to about 20 pounds of the inhibitor per ton of 66 B. sulfuric acid.

The pickling or cleaning operation may be carried out as in usual practice. be completely immersed in the acid, or a solution of the pickling bath may be sprayed onto the surface of the metal and subsequently removed with a water spray. The concentration of the acid bath and the temperature of the solution may be varied as desired, and the inhibitors may ,be added to the pickling baths in greater or less proportion than mentioned above. sulfuric and hydrochloric acids are 'generally employed in pickling operations, although any other nonoxidizing acid may be substituted in whole or in part. Pickling solutions may contain acids such as phosphoric or hydroiluoric acids. Acid concentrations usually employed in commercial practice, for example 6 to 12%, are generally preferred in carrying out the present invention.

The inhibiting properties of the improved sulfur oil inhibitors of the invention are demonstrated by the following. In these representative tests, the pickling bath comprised a 5% H2504 solution containing 0.1% by volume of the inhibitor. Mild steel strips of 1/3 inch thickness were used, and the temperature of the pickling solution maintained at 160 F. The strips were subjected to a half hour preliminary pickling treatment and, after dryingand weighing, were subjected to a further pickling treatment in the same solution for an hour and a half, dried and again weighed. Results obtained were as follows:

Loss in Loss in weight y weight 1% hour run hour run Grams Gram@ Inhibitor A.. 0.0122 0. 0131 Inhibitor B .0858 .0082 No inhibitor use 2. 0879 2. 9799 The metal may BEST AVAILABLE COPY vention. involves provision of acid solutions inhibited sulciently to prevent corrosion of metal surfaces by the acid, For example, in the transportation or storage of corrosive mineral acids in metal containers or pipe lines, a relatively small amount Aof inhibitor may be added to the acid to prevent corrosion of confining metal surfaces. The amount of inhibitor used will depend upon the nature and concentration of the acid solution.

Instead of decomposing the acid sludge by heating as described in connection with the drawing, the original acid sludge may be subjected to hydrolysis as by steaming with live steam, for say an hour,'until separation of weak acid (sludge acid) and an upper tar layer takes place. The weak acid may be drawn off and the resulting acid tar or sludge material treated as by heating as in a retort Il. The oily distillate may be taken in two or more cuts if desired, although it is preferred to collect the oily distillate as in a tank 26. During steaming of the acid sludge a light colored distillate may be recovered in a suitable container. This distillate and the condensate collecting in tank 26 may- 'tures less than about 650 F., stable with respect to sulfur deposition, substantially free of free sulfur, containing alkyl sulfides, having a sulfur content not less than about'3% and formed by dissociating sludge material, resulting from sulfuric acid treatment of hydrocarbon distillate oils obtained from sulfur containing crudes, with aid of heat at temperatures not more than about '750 F. to break up the sludge under conditions to form a hot gas mixture containing hydrocarbon vapors, and cooling the gas mixture to form an oily condensate boiling at temperatures less than about 650"v F.

2. The process of pickling metals which comprises subjecting the metal to the action of a bath containing a solution of a mineral acid and a relatively small amount of a corrosion inhibitor comprising a relatively light-bodied, light-colored,

low viscosity sulfur oil boiling at temperatures less than about 650 F., stable with respect to sulfur deposition, substantially free of free sulfur, containing alkyl sulildes, having a sulfur content not less than about 3% and formed by dissociating sludge material,resulting from sulfuric acid treatment of hydrocarbon distillate oils obtained from sulfur containing crudes, With aid of heat at temperatures not more than about 750 F. to break up the sludge under conditions to form a hot gas mixture containingwater and hydrocarbon vapors, cooling the gas mixture to form a condensate comprising water and oil, separating water from oil, distilling the oil, and recovering as condensate oil boiling at temperatures less than about 650 F. 3. The process of pickling metals which comprises subjecting the metal to the action of a bath containing a solution of a mineral acid and a relatively small amount of a corrosion inhibitor comprising a relatively light-bodied, light-colored, low viscosity sulfur oil boiling at temperatures less than about 650 F., stable with respect to sulfur deposition, substantially free of free sulfur, containing alkyl suliides,l having a sulfur content not less than about 3% and formed by dissociating sludge material, resulting from sulfuric acid treatment of hydrocarbon distillate oils obtained from sulfur containing crudes, with aid of heat at temperatures not more than about '750 F; to break up the sludge under conditions to form a hot gas mixture containing water and hydrocarbon vapors, cooling the gas mixture to form a condensate comprising water and oil, separating water from oil, distilling the oil, recovering as condensate oil boiling at temperatures less than about 650 F., and stabilizing the oil.

4. The process of piclnng metals which comprises subjecting the metal to the action of a bath containing a solution of a mineral acid and a relatively small amount of a corrosion inhibitor comprising a relatively light-bodied, light-colored, low viscosity sulfur oil boiling at temperatures less than about 650 F., stable with respect to sulfur deposition, substantially free of free sulfur, containing alkyl suliides, having a sulfur content vnot less than about 3% and formed by dissociating sludge material, resulting from sulfuric acid treatment of hydrocarbon distillate oils containing not less than about 0.15% sulfur, with aid of heat at temperatures not more than about '150 F. to break up the sludge under conditions to form a hot gas mixture containing hydrocarbon vapors, and cooling the gas 'mixture to form an oily condensate boiling attemperatures less than about 650 F.

5. The process of pickling metals which comprises subjecting the metal to the action of a bath containing a solution of a mineral acid and a relatively small amount of a corrosion inhibitor comprising a relatively light-bodied, light-colored, low viscosity sulfur oil boiling at temperatures not more than about 350 F., stable with respect to sulfur deposition, substantially free of free sulfur, containing alkyl suldes, having a sulfur content not less than about 3% and formed by dissociating sludge material, resulting from sulfuric acid treatment of hydrocarbon distillate oils Yobtained from sulfur containing crudes, with aid of heat at temperatures not more than about '150 F. to break up the sludge under conditions to form a hot gas mixture containing water and hydrocarbon vapors, cooling the gas mixture to form a condensate comprising water and oil, separating water from oil, distilling the oil, and recovering as condensate a fraction boiling at temperatures not more than about 350 F.

6. The process of pickling metals which comprises subjecting the metal to the action of a bath containing a solution of a mineral acid and a relatively small amount of a corrosion inhibitor comprising a relatively light-bodied, lightcolored, low viscosity sulfur oil boiling substantially within the range 350 F. to 650 F., stable with respect to sulfur deposition, substantially free of free sulfur, containing alkyl suldes, having a sulfur content not less than about 3% and formed by dissociating sludge material, resulting from sulfuric acid treatment of hydrocarbon distillate oils obtained from sulfur containing crudes, with the aid of heat at temperatures not more than about r150" F. to break up the sludge under conditions to form a hot gas mixture containing water and hydrocarbon vapors, cooling the gas mixture to form a condensate comprising water and oil, separating water from oil, dis- BEST AVAILABLE COPY 5 tilling the oil, and recovering as condensate a fraction boiling substantially Within the range 350 F. to 650 F. g

'7. A pickling bath for metals comprising a solution of mineral acid and a relatively small amount of a corrosion inhibitor comprising a relatively light-bodied, light-colored, low viscosity sulfur oil boiling at temperatures less than about 650 F., stable with respect to sulfur deposition, substantially free of free sulfur, containing alkyl suldes, having a sulfur content not less than about 3% and formed by dissociating sludge material, resulting from sulfuric acid treatment of hydrocarbon distillate oils obtained from sulfur containing crudes, with aid of heat at temperatures not more than about 750 F. to break up the sludge under conditions to form a hot gas mixture containing hydrocarbon vapors, and cooling the gas mixture to form an oily condensate boiling at temperatures less than about 650 F.

8. A pickling bath for metals comprising a solution of mineral acid and a relatively small amount of a corrosion inhibitor comprising a relatively light-bodied, light-colored, low viscosity sulfur oil boiling at temperatures less than about 650 F., stable with respect to sulfur deposition, substantially free of free sulfur, containing alkyl sulfides, having a sulfur content not less than about 3% and formed by dissociating sludge material, resulting from sulfuric acid treatment of hydrocarbon distillate oils obtained from sulfur containing crudes, with aid of heat at temperatures not more than about 750 F. to break up the sludge under conditions to form a hot gas mixture containing Water-and hydrocarbon vapors, cooling the gas mixture to form a condensate comprising water and oil, separating water from oil, distilling the oil, and recovering as condensate oil boiling at temperatures less than about 650 F.

9. A pickling bath for metals comprising a solution of mineral acid and a relatively small amount of a corrosion inhibitor comprising a relatively light-bodied, light-colored, low viscosity sulfur oil boiling at temperatures not more than about 350 F., stable with respect to sulfur deposition, substantially free of free sulfur, containing alkyl sulfides, having a sulfur content not less than about 3% and formed by dissociating sludge material, resulting from sulfuric acid treatment of hydrocarbon distillate oils obtained from sulfur containing crudes, with aid of heat at temperatures not more than about 760 F. to break up the sludge under conditions. to form a hot gas mixture containing water and hydrocarbon vapors, cooling the gas mixture to form a condensate comprising water and oil, separating water from oil, distilling the oil, and recovering as condensate a fraction boiling at temperatures not more than about 350 F.

l0. A pickling bath for metals comprising a solution of mineral acid and a relatively small` hot gas mixture containing water and hydrocarbon vapors, cooling the gas mixture to form a condensate comprising water and oil, separating water from oil. distilling the oil, and recovering as condensate a fraction boiling substantially Within the range 350 F. to 650 F.

1l. A mineral acid solution substantially noncorrosive to metals comprising mineral acid of concentration corrosive to metal and containing a sulfur bearing oil corrosion inhibitor, said solution being adapted for utilization in operations comprising metal pickling, storage of said solution within confining metal surfaces, and passage of said solution through coniining metal surfaces, and said solution containing said oil in quantity suilicient to substantially inhibit corrosive action of the acid on metal; said inhibitor @EST AVAILABLE COPY comprising a relatively light-bodied, light-c01- o-red, low viscosity sulfur oil boiling at temperatures less than about 650 F., stable with respect to sulfur deposition, substantially free'of free n sulfur, containing alkyl sulfides, having a sulfur content not less than about 3% and formed by dissociating sludge material, resulting from sulfuric acid treatment of hydrocarbon distillate oils obtained from sulfur containing crudes, with aid of heat at temperatures not more than about 750 F. to break up the sludge under' conditions to form a hot gas mixture containing hydrocarbon vapors, and cooling the gas mixture to form an oily condensate boiling at temperatures less than about 650 F.

J. ROSS TUTI'LE. 

